Surgical Navigation System And Method

ABSTRACT

The present disclosure relates to a surgical navigation system for the alignment of a surgical instrument and methods for its use, wherein the surgical navigation system may comprise a head-mounted display comprising a lens. The surgical navigation system may further comprise tracking unit, herein the tracking unit may be configured to track a patient tracker and/or a surgical instrument. Patient data may be registered to the patient tracker. The surgical instrument may define an instrument axis. The surgical navigation system may be configured to plan one or more trajectories based on the patient data. The head-mounted display may be configured to display augmented reality visualization, including an augmented reality position alignment visualization and/or an augmented reality angular alignment visualization related to the surgical instrument on the lens of the head-mounted display.

RELATED APPLICATIONS

This application is a national stage of International Application No.PCT/IB2018/053130, filed on May 4, 2018, which claims priority to andthe benefit of European Patent Application No. 17169700.6, filed on May5, 2017, the entire contents of both of which are hereby incorporated byreference in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to a surgical navigation systemfor supporting surgical interventions. More specifically, but notexclusively, the present disclosure relates generally to a holographicsurgical navigation system.

BACKGROUND

Computer-assisted surgery, including surgical navigation systems, is agrowing trend in the medical field. The surgical navigation system, incombination with pre-operative images and/or patient data may beutilized during a surgical intervention to support the surgeon inexecuting a medical procedure. For that purpose, image guidance surgicalnavigation systems are used for open and minimally-invasive surgicalinterventions, such as spine, joint, and/or neuro surgery. The aim ofsuch surgical navigation systems is to determine the position of asurgical instrument used by the surgeon that can be illustrated orvisualized in the pre-operative images and/or patient data correspondingto the patient's anatomy. Continuous detection of the position and/ororientation (i.e., pose) of the patient and/or the surgical instrument(so-called navigation data) are necessary to provide an accurate spatialrepresentation of the surgical instrument relative to the patient.

The surgical navigation system may also visualize the position and/oralignment of a medical device or implant to the surgeon, such as theposition and alignment of a pedicle screw for multiple vertebra fixationin the context of spine surgery. During operation, the surgicalnavigation system may provide a visualization to the surgeon, allowingthe surgeon to see an overlay of the position of the surgical instrumentand/or the medical device/implant projected exactly on an image orvisualization of the patient.

Taking existing solutions into account, it is to be noted that knownsurgical navigation solutions do not sufficiently address the surgicalnavigation system guidance and alignment of surgical instruments. Afurther disadvantage of existing solutions is that the visualization isdetached from the surgical site, forcing a deviation of attention of thesurgeon.

Thus, there is a need for new surgical navigation systems addressingthese disadvantages.

SUMMARY

In an exemplary configuration of a surgical navigation system and methodof aligning a surgical instrument, the surgical navigation system may beconfigured to provide an augmented reality visualization during amedical intervention. Generally, the surgical navigation system maycomprise a tracking unit. The tracking unit may comprise one or moreposition sensors. The surgical navigation system may further comprise ahead-mounted display, patient tracker, and a surgical instrument, eachof which may comprise one or more tracking members or makers configuredto be detected by the one or more position sensors of the tracking unit.The tracking unit may be configured to continuously track the positionand/or orientation (pose) of the head-mounted display, patient tracker,and surgical instrument within a localized or common coordinate system.The surgical navigation system may be further configured to register theposition and/or orientation of the head-mounted display, patienttracker, and surgical instrument with patient data to generate anddisplay an augmented reality visualization on a lens or screen of thehead-mounted display. The augmented reality visualization may comprisethe surgical instrument and/or a target trajectory axis overlaid onpatient data, wherein the patient data may comprise pre-operative imagesof the patient's anatomy and/or or target objects. The target object(s)may comprise the planned surgical pathway, a planned position for animplant or medical device, and/or an anatomical feature of the patient.

The augmented reality visualization may comprise a position alignmentvisualization and/or an angular alignment visualization. The navigationsystem may be configured to display the position alignment visualizationand/or the angular alignment visualization on the head-mounted displaysuch that the visualizations are overlaid on the actual patient from theperspective of the surgeon to create a 3-D or holographic visualization.

In another example configuration of an augmented reality system, theaugmented reality system may comprise a surgical navigation system, apatient tracker trackable by said surgical navigation system, and asurgical instrument trackable by said surgical navigation system. Theaugmented reality system may further comprise a head-mounted displaycomprising a lens and a controller configured to display an augmentedreality position alignment visualization as two axis-aligned deviationvectors comprising a decomposition of a distance vector from a targetpoint on a target trajectory axis to the surgical instrument on saidlens.

In yet another example configuration of an augmented reality system, theaugmented reality system may comprise a head-mounted display including alens. The augmented reality system may also comprise a surgicalnavigation system comprising a tracking unit configured to track anumber of objects positioned within a defined field or coordinatesystem, such as a surgical field. The augmented reality system may alsoinclude a patient tracker registered to patient data and trackable bysaid surgical navigation system, and a surgical instrument having aninstrument tracker trackable by said surgical navigation system. Theinstrument tracker may be configured to define an instrument axis of thesurgical instrument. The augmented reality system may also comprise acontroller configured to generate an augmented reality positionalignment visualization as two axis-aligned deviation vectors comprisingthe decomposition of a distance vector from a target point on a targettrajectory axis to a point on the surgical instrument to display on saidlens of said head-mounted display.

In yet another example configuration of an augmented reality system, asurgical navigation system may include a patient tracker and a surgicalinstrument tracker. The surgical navigation system may be configured toplan a target trajectory axis based on patient data and for thealignment of a tip of a surgical instrument with the target trajectoryaxis. The surgical navigation system may further comprise a head-mounteddisplay comprising a head-mounted display tracker, wherein thehead-mounted display is configured to display an augmented realityposition alignment visualization comprising two axis-aligned deviationvectors comprising the decomposition of a distance vector from a pointon the target trajectory axis to the tip of the surgical instrument. Thehead-mounted display may further be configured to display an augmentedreality angular alignment visualization comprising a deviation anglewhich represents the angle between a first direction vector of theinstrument axis and a second direction vector of the target trajectoryaxis.

An exemplary method of displaying surgical navigation information maycomprise a head-mounted display with a surgical navigation systemincluding a surgical instrument having a tip in view of a surgical planincluding a target trajectory axis. The method may comprise the step ofdisplaying an augmented reality position alignment visualizationcomprising two axis-aligned deviation vectors on a head-mounted display,said two-axis aligned deviation vectors comprising a first vector and asecond vector wherein the first vector and second vector arerepresentative of the decomposition of a distance vector from a point onthe target trajectory axis to the tip of the surgical instrument. Themethod may further comprise the step of updating the augmented realityposition alignment visualization displayed on the head-mounted displayto indicate a relative location of the surgical instrument to the targettrajectory axis from the perspective of the head-mounted display.

Another exemplary method of aligning a surgical instrument may comprisea surgical navigation system, wherein the surgical navigation systemincludes a tracking unit configured to track the position of ahead-mounted display, a patient tracker, and a surgical instrumenttracker. The surgical navigation system may further be configured toplan a target trajectory axis based on patient data registered to thepatient tracker. The method of aligning the surgical instrument maycomprise the step of displaying on the head-mounted display an augmentedreality position alignment visualization as two axis-aligned deviationvectors comprising the decomposition of a distance vector from a pointon the target trajectory axis to a tip of the surgical instrument. Themethod may further comprise the step of displaying on the head-mounteddisplay an augmented reality angular alignment visualization comprisinga deviation angle which shows the angle between a first direction vectorof the axis of the surgical instrument and a second direction vector ofthe target trajectory axis. The method may further comprise the step ofcontinuously updating the augmented reality position alignmentvisualization and/or the augmented reality angular alignmentvisualization displayed on the head-mounted display based on thetracking unit to indicate the relative location of the surgicalinstrument to the target trajectory axis from the perspectives of thehead-mounted display.

It is an advantage of the proposed apparatus and method to make medicalinterventions more effective, safer, and more precise.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present disclosure will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingswherein:

FIG. 1A is a perspective view of a surgeon using a first configurationof a surgical navigation system including a head-mounted display and asurgical tracking unit.

FIG. 1B is a schematic view of a control system for the surgicalnavigation system of FIG. 1A.

FIG. 2 is a perspective view of a patient tracker of the surgicaltracking unit of FIG. 1A, the patient tracker coupled to a patientproximate to a region of interest.

FIG. 3 is a schematic view of a first configuration of an augmentedreality visualization projected on the lens of the head-mounted displayof FIG. 1A, the augmented reality visualization projected on the lensincluding virtual images overlaid on live features that are illustratedin phantom.

FIG. 4 is a schematic view of a second configuration of an augmentedreality visualization projected on the lens of the head-mounted displayof FIG. 1A, the augmented reality visualization projected on the lensincluding virtual images overlaid on live features that are illustratedin phantom.

FIG. 5 is an enhanced view of an exemplary augmented realityvisualization as depicted on the head-mounted display during a surgicalprocedure including the surgical tool.

FIG. 6 is an enhanced view of a second exemplary augmented realityvisualization as observed by the user on the head-mounted display duringa surgical procedure including the patient tracker and a slice of apre-operative image.

FIG. 7 is a schematic view of a third configuration of an augmentedreality visualization projected on the lens of the head-mounted displayof FIG. 1A, the augmented reality visualization projected on the lensincluding a virtual image of pre-operative data illustrated in a displaywindow.

FIG. 8 is a schematic view of a fourth configuration of an augmentedreality visualization projected on the lens of the head-mounted displayof FIG. 1A, the augmented reality visualization projected on the lensincluding a virtual image of pre-operative data.

DETAILED DESCRIPTION

FIGS. 1A and 1B illustrate an exemplary configuration of a surgicalnavigation system 20, which may include a tracking unit 10 and ahead-mounted display 30. The surgical navigation system 20 may beutilized by a surgeon to assist the surgeon in executing a medicalprocedure, such as inserting a pedicle screw as part of a multiplevertebrae fixation or removing a brain tumor.

The surgical navigation system 20 may comprise a navigation interfacethat includes one or more user inputs I and one or more displays 22. Theuser input I may be configured to allow the surgeon to input or enterpatient data. The patient data may comprise patient images, such aspre-operative images of the patient's anatomy. These images may be basedon MRI scans, radiological scans or computed tomography (CT) scans ofthe patient's anatomy. The patient data may also include additionalinformation related to the type of medical procedure being performed,the patient's anatomical features, the patient's specific medicalcondition, and/or operating settings for the surgical navigationsettings. For example, in performing a spinal surgery, the surgeon mayenter information via the user input I related to the specific vertebraethe medical procedure is being performed on. The surgeon may also inputvarious anatomical dimension related to the vertebrae and/or the sizeand shape of a medical device or implant to be inserted during themedical procedure.

The display 22 of the surgical navigation system 20 may be configured todisplay various prompts or data entry boxes. For example, the display 22may be configured to display a text box or prompt that allows thesurgeon to manually enter or select the type of surgical procedure to beperformed. The display 22 may also be configured to display patientdata, such as a pre-operative image or scan. As described above, thepre-operative image may be based on MRI scans, radiological scans orcomputed tomography (CT) scans of the patient's anatomy. Thepre-operative image may be uploaded to the surgical navigation systemand displayed on the display 22. The display 22 may be furtherconfigured to display a surgical plan for a medical procedure overlaidon the patient data or image. The surgical plan may include a surgicalpathway for executing a medical procedure or a planned trajectory ororientation for the medical instrument during the medical procedure. Thesurgical plan may also include overlaying the position and/ororientation of an implant or medical device to be inserted during themedical procedure on the patient data or image.

The surgical navigation system 20 may further comprise a navigationcontroller 80. The navigation controller 80 can be a personal computeror laptop computer. The navigation controller 80 may be in communicationwith the user input I, display 22, central processing unit (CPU) and/orother processors, memory (not shown), and storage (not shown). Thenavigation controller 80 may further comprise software and/or operatinginstructions related to the operation of the surgical navigation system20. The software and/or operating instructions may comprise planningsystem configured to find an accurate position and/or angular alignmentof the surgical instrument 50 in relation to the patient 60. Thenavigation controller 80 may be in wired or wireless communication withthe head-mounted display. Accordingly, the head-mounted display 30 mayinclude a wireless or wired transceiver.

The surgical navigation system 20 may further comprise a tracking unit10. The tracking unit 10 may also be referred to as a tracking system orcamera unit. The tracking unit 10 may comprise a housing 12 comprisingan outer casing that houses one or more position sensors 14. Theposition sensors may comprise cameras, such as charge-coupled devices(CCD) cameras, CMOS cameras, and/or optical image cameras,electromagnetic sensors, magnetoresistance sensors, radio frequencysensors, or any other sensor adapted to sufficiently sense the positionof a navigation marker. In some configurations, at least two positionsensors 14 may be employed, preferably three or four. For example, theposition sensors 14 may be separate CCDs. In one configuration three,one-dimensional CCDs are employed. Two-dimensional or three-dimensionalsensors could also be employed. It should be appreciated that in otherconfigurations, separate tracking units 10, each with a separate CCD, ortwo or more CCDs, could also be arranged around the operating room. TheCCDs detect light signals, such as infrared (IR) signals.

The housing 12 of the tracking unit 10 may be mounted on an adjustablestand or arm to allow for repositioning of the position sensor(s) 14.For example, the adjustable stand or arm may be configured to allow forrepositioning of the position sensor(s) 14 to provide an optimal view ofthe surgical field that ideally is free from obstructions.

The tracking unit 10 may include a sensor controller (not shown) incommunication with the position sensors 14, such as optical sensors 14,and configured to receive signals from the optical sensors 14. Thesensor controller may communicate with the navigation controller 80through either a wired and/or wireless connection. One such connectionmay be the RS-232 communication standard or the IEEE 1394 interface,which are serial bus interface standards for high-speed communicationsand isochronous real-time data transfer. The connection could also use acompany-specific protocol or network protocols such as UDP or TCP. Inother embodiments, the optical sensors 14 may be configured tocommunicate directly with the navigation controller 80.

The tracking unit 10 in communication with the surgical navigationsystem 20 via the navigation controller 80 may be used to determine therelative position of the head-mounted display 30, a surgical instrument50, and a patient 60 or region of interest 62. Utilizing the relativeposition of the head-mounted display 30, the one or more surgicalinstruments 50, and the patient 60, the navigation controller 80 of thesurgical navigation system 20 is thus able to compute augmented reality(AR) visualizations that may be displayed in the head-mounted display 30in registration with the patient 60 and the head-mounted display 30.

The surgical instrument 50 may comprise one or more instrument markers52 configured to be detectable by the position sensors 14 of thetracking unit 10. The surgical instrument 50 may be configured tocomprise passive tracking elements or instrument markers 52 (e.g.,reflectors) for transmitting light signals (e.g., reflecting lightemitted from the tracking unit 10) to the position sensor(s) 14.Alternatively, the instrument markers 52 may comprise a radio opaquematerial that is identified and trackable by the position sensor(s) 14.In other configurations, active tracking markers can be employed. Theactive tracking markers can be, for example, light emitting diodestransmitting light, such as infrared light. Active and passivearrangements are possible. The instrument markers 52 may be arranged ina defined or known position and orientation relative to the otherinstrument markers 52 in order to allow the surgical navigation system20 to determine the position and orientation (pose) of the surgicalinstrument 50. For example, the instrument markers 52 may be registeredto the surgical instrument 50 to allow the surgical navigation system 20to determine the position and/or orientation of a tip 54 or tool portionof the surgical instrument 50 within a defined space, such as thesurgical field.

The surgical navigation system 20 may further comprise a patient tracker40, wherein the patient tracker 40 may be configured to localize apatient 60 in space, such as the surgical field. The patient tracker 40may comprise an attachment member 44 configured to secure the patienttracker 40 to the patient 60. The attachment member 44 may comprise aclamp, adhesive, strap, threaded fastener, or other similar attachmentdevice. For example, the attachment member 44 may comprise a clampconfigured to be secured to the patient 60. This may include utilizing aclamp to secure the patient tracker 40 to a vertebra of the patient 60proximate to a region of interest 62. This may allow the tracking unit10 to determine the position and/or orientation of the patient's spineduring spinal surgery. Alternative, the attachment 44 may comprise astrap, wherein the strap is configured to encircle and secure thepatient tracker to the patient's head. This may allow the trackingsystem to determine the position and/or orientation of the patient'shead during neurosurgery.

The patient tracker 40 may further comprise one or more patient markers42 configured to be detectable by the position sensors 14 of thetracking unit 10. The patient tracker 40 may be configured to comprisepassive tracking elements or patient markers 42 (e.g., reflectors) fortransmitting light signals (e.g., reflecting light emitted from thetracking unit 10) to the position sensor(s) 14. Alternatively, thepatient markers 42 may comprise a radio opaque material that isidentified and trackable by the position sensor(s) 14. The patientmarkers 42 may be arranged in a defined or known position andorientation relative to the other patient markers 42 in order to allowthe surgical navigation system 20 to determine the position andorientation (pose) of the patient 60 and/or region of interest 62. Inother configurations, active tracking markers can be employed. Theactive markers can be, for example, light emitting diodes transmittinglight, such as infrared light. Active and passive arrangements arepossible. The patient markers 42 may be arranged in a defined or knownposition and orientation relative to the other patient markers 42 inorder to allow the surgical navigation system 20 to determine theposition and orientation (pose) of the patient 60 and/or region ofinterest 62.

Referring to FIGS. 1A and 1B, the head-mounted display (HMD) 30 may beemployed in addition to or as an alternative to one or more of thedisplay(s) 22 to enhance visualization before, during, and/or aftersurgery. The HMD 30 can be used to visualize the same objects describedas being visualized on the display(s) 22 and can also be used tovisualize other objects, features, instructions, warnings, etc. The HMD30 can be used to assist with locating and or visualizing target objectsrelated to the medical procedure. The HMD 30 can also be used tovisualize instructions and/or warnings, among other uses, as describedfurther below.

The HMD 30 may be a HoloLens® provided by Microsoft Corporation, whichis referred to as a mixed or augmented reality HMD owing to its overlayof augmented reality visualizations or computer-generated images ontothe real world. It should be appreciated that any reference to augmentedreality encompasses mixed reality. Thus, in the configuration describedherein, the HMD 30 provides a computational holographic display. Othertypes of mixed/augmented reality HMDs may also be used, such as thosethat overlay computer-generated images onto video images of the realworld. The HMD 30 may comprise a cathode ray tube display, liquidcrystal display, liquid crystal on silicon display, or organiclight-emitting diode display. The HMD 30 may comprise see-throughtechniques like those described herein comprising a diffractivewaveguide, holographic waveguide, polarized waveguide, reflectivewaveguide, or switchable waveguide.

The HMD 30 comprises a head-mountable structure 32, which may be in theform of an eyeglass and may include additional headbands 38 or supportsto hold the HMD 30 on the user's head. In other embodiments, the HMD 30may be integrated into a helmet or other structure worn on the user'shead, neck, and/or shoulders.

The HMD 30 has a visor 32 and a lens/waveguide 36 arrangement. Thelens/waveguide 36 arrangement is configured to be located in front ofthe user's eyes when the HMD 30 is placed on the user's head. Thewaveguide transmits the augmented reality visualizations or images (alsoreferred to as computer-generated images, virtual images, or holographicimages) to the user's eyes while at the same time, real images may beseen through the lens/waveguide 36 (it being transparent) such that theuser sees a mixed or augmented reality including both real and virtualobjects.

Referring to FIG. 1B, the HMD 30 may further comprise a head-mounteddisplay controller (HMD controller) 180 that is configured to be incommunication with the navigation controller 80 of the surgicalnavigation system 20. The HMD controller 180 may comprise an imagegenerator that may be configured to generate the augmented realityvisualizations and that transmits those visualizations to the userthrough the lens/waveguide 36 arrangement. The HMD controller 180 maycontrol the transmission of the augmented reality visualizations to thelens/waveguide 36 arrangement of the HMD 30. The HMD controller 180 maybe a separate computer that is located remote from the HMD 30.Alternatively, the HMD controller 180 may be integrated into thehead-mountable structure 32 of the HMD 30. The HMD controller 180 may bea laptop computer, desktop computer, microcontroller, or the like withmemory, one or more processors (e.g., multi-core processors), inputinputs I, output devices (fixed display in addition to HMD 30), storagecapability, etc.

The HMD 30 comprises one or more head-mounted display markers or HMDmarkers 34 that are configured to be detectable by the positionsensor(s) 14 of the tracking unit 10. The HMD 30 may be configured tocomprise passive tracking elements or HMD markers 34 (e.g., reflectors)for transmitting light signals (e.g., reflecting light emitted from thetracking unit 10) to the position sensor(s) 14. Alternatively, the HMDmarkers 34 may comprise a radio opaque material that is detectable andtrackable by the position sensor(s) 14. In other configurations, activetracking markers can be employed. The active markers can be, forexample, light emitting diodes transmitting light, such as infraredlight. Active and passive arrangements are possible. The HMD markers 34may be arranged in a defined or known position and orientation relativeto the other HMD markers 34 in order to allow the surgical navigationsystem 20 to determine the position and orientation (pose) of the HMD 30within a defined area, such as the surgical field.

The HMD 30 may also comprise a photo and/or video camera 170 incommunication with the HMD controller 180. The camera 170 may be used toobtain photographic or video images with the HMD 30, which can be usefulin identifying objects or markers attached to objects, as will bedescribed further below.

The HMD 30 may further comprise an inertial measurement unit (IMU) 176in communication with the HMD controller 180. The IMU 176 may compriseone or more 3-D accelerometers, 3-D gyroscopes, and other sensors toassist with determining a position and/or orientation of the HMD 30 inthe HMD coordinate system or to assist with tracking relative to othercoordinate systems. The HMD 30 may also comprise an infrared motionsensor 178 to recognize gesture commands from the user. Other types ofgesture sensors are also contemplated. The infrared motion sensor 178may be arranged to project infrared light or other light in front of theHMD 30 so that the infrared motion sensor 178 is able to sense theuser's hands, fingers, or other objects for purposes of determining theuser's gesture command and controlling the HMD 30, HMD controller 180,and/or navigation controller 80, accordingly.

While FIG. 1A only includes a single individual or surgeon wearing anHMD 30, it is further contemplated that a plurality of HMDs 30 may beconfigured to be in communication with the surgical navigation system20. For example, an entire surgical team may wear HMDs 30. In someconfigurations, such as those in which video cameras 170 are integratedinto the HMDs 30 to provide point of view (POV) video, through the POVvideo stream analysis or simpler context awareness mechanisms (e.g.,sensory-based feedback, heuristics based on inputs from isolatedsensors, etc.), a computer-based model of the surgical context canprovide participant-specific mixed/augmented reality aids to facilitatethe current task being performed by the individual participant or helpprepare for their next contribution to the surgical or medicalprocedure.

In one configuration, two or more participants and their HMDs 30 can belinked together in conjunction with the contextual information of themedical procedure. The participants may be linked by sharing theircurrent POV or in a more inherent way, by sharing the objects ofinterest being addressed at any given point in time by any of theparticipants. Within this configuration, a first participant is able toenhance his or her personal assessment of a second participant'scircumstances through the display of mixed/augmented reality aids as thefirst participant directs his/her personal POV to that of the secondparticipant. As the first participant realizes an opportunity foroptimization or altering the planned medical procedure, the appropriateinterplay with the different participants or surgical environment cantake place. This interaction can be directly executed by the firstparticipant or can be facilitated through mixed/augmented reality aidsor other computer-assisted aids, which in turn can be automaticallygenerated or created by the first participant to support the secondparticipant's course of action.

Referring to FIG. 2, an example representation of an augmented realityvisualization of the region of interest 62 as perceived by the userthrough the lens 36 of the HMD 30 is illustrated. As illustrated in FIG.2, the patient tracker 40 may be coupled or secured to the patient 60via the attachment member 44. This will allow the tracking unit 10 toidentify the position and/or orientation of the patient 60 and/or regionof interest 62 relative to the HMD 30 for the purpose of generating andorienting the appropriate augmented reality visualization on the lens 36so that the virtual portion of the image may be properly overlaid on thereal portion of the patient 60 as viewed through the lens 36. While onlya single patient tracker 40 is illustrated in FIGS. 1A and 2, it isfurther contemplated that additional patient trackers 40 may be coupledto or attached to the patient 60. The use of additional patient trackers40 may allow the position and/or movement of multiple portions of thepatient 60 and/or regions of interest 62 to be tracked. The use ofmultiple patient trackers 40 may also increase the accuracy of trackingthe position and/or movement of the patient 60 and/or region of interest62.

The augmented reality visualization of the region of interest 62 maycomprise both an augmented reality boundary visualization and/orcombined boundary with augmented reality textual label. For example, asillustrated in FIG. 2, augmented reality boundary visualizations areshown as cubes enclosing individual vertebrae as projected or displayedon the lens 36 of the HMD 30, as viewed by the user when observing thepatient's 60 actual spine through the lens 36. The augmented realityboundary visualizations may further be identified to the user on thelens 36 of the HMD 30 by the augmented reality textual labels, such asL1. For example, as illustrated in FIG. 2, “L1” is included in theaugmented reality visualization projected on the lens 36 of the HMD 30to identify the specific vertebrae enclosed by the augmented realityboundary visualization. While only a single augmented reality textuallabel is illustrated in FIG. 2, it should be understood that a pluralityof additional augmented reality textual labels may be included as partof the augmented reality visualization to label and/or identifyadditional features or objects to the user of the HMD 30.

Referring to FIG. 3, an additional configuration of the augmentedreality visualization as perceived by the user through the lens 36 ofthe HMD 30 is illustrated. In the example configuration illustrated inFIG. 3, the user is viewing a portion of the patient's 60 head throughthe lens 36 of the HMD 30. For example, FIG. 3 may represent theaugmented reality visualization as seen by a surgeon performing aneurosurgery procedure, such as removing a tumor. Within the lens 36,the items illustrated in phantom, i.e., using dotted lines, representthe real features that may be seen by the user. This may include aportion of the patient's 60 head, as well as an incision site or regionof interest 62. The user may also be able to see a portion of thepatient tracker 40, attachment member 44, and/or the patient markers 42through the lens 36 of the HMD 30.

The user of the HMD 30 may also observe a number of augmented realityvisualizations, which are illustrated within the lens 36 of FIG. 3 usingsolid lines. One such augmented reality visualization may include atarget object representing a single point-shaped landmark related to themedical procedure. For example, as illustrated in FIG. 3, the targetobject 130 may represent an item within the patient 60 that is to beoperated on during the medical procedure, such as a tumor or organ.Alternatively, the target object 230 may represent a medical device orimplant to be inserted in the patient 60 during the medical procedure,which will be discussed in detail below.

The augmented reality visualization may also comprise a targettrajectory axis 210. The target trajectory axis 210 may represent aplanned or intended surgical path. For example, the target trajectoryaxis 210 may represent the optimal or preferred angle or direction foraligning and/or inserting the surgical instrument 50 during execution ofthe medical procedure. The target trajectory axis 210 may be defined bya solid or intermittent line connecting a target object 130, 230 and anentry point or insertion point proximate to the region of interest 62.

The augmented reality visualization may further comprise an augmentedreality window, indicator, or text box 310. The augmented reality window310 may comprise a window displayed on the lens 36 of the HMD 30. Theaugmented reality window 310 may be configured to display the patientdata, such as a pre-operative image or scan. The augmented realitywindow 310 may also be configured to display an image of the plannedsurgical procedure, including identifying any critical items such asnerves, organs, or similar elements the user may want to be aware ofwhen performing the medical procedure. For example, when inserting ascrew in the patient's 60 vertebrae, the image may include nerve endingsto avoid. The augmented reality window 310 may also include text orindicia related to the medical procedure. For example, the augmentedreality window 310 may include notes related to the medical procedure,such as facts specific to the patient's 60 medical condition.Alternatively, the augmented reality window 310 may also include text ofinformation related to the distance the surgical instrument 50 is fromthe patient 60, the region of interest 62, the target object 130, 230,and/or the target trajectory axis 210.

The augmented reality visualization may also comprise one or morecontrol buttons 320, 322, 324 to be displayed on the lens 36 of the HMD30. The one or more control buttons 320, 322, 324 may be configured toallow the user to manipulate the augmented reality visualizationdisplayed on the lens 36. For example, the user may use hand and/orfacial gestures or movements, as described above, to select or activateone of the control buttons 320, 322, 324. The control buttons 320, 322,324 may be configured to adjust the contrast, transparency, and/or colorof the augmented reality visualization on the lens 36. The controlbuttons 320, 322, 324 may also be used to manipulate or enhance theinformation displayed on the lens 36. For example, the control buttons320, 322, 324 may be configured to zoom in and/or zoom out on thepatient data displayed in the augmented reality window 310. This mayinclude zooming in on a pre-operative image or scan of the patient 60 toallow the user to better visualize the area proximate to the targetobject 130, 230. The control buttons 320, 322, 324 may further beconfigured to rotate or move an image of the patient data. This mayinclude moving the position and/or location the augmented reality window310 is displayed on the lens 36 to avoid blocking or interfering withthe user's view of the augmented reality visualization on the patient60.

FIG. 4 comprises another configuration of the augmented realityvisualization as perceived by the user through the lens 36 of the HMD 30including the surgical instrument 50. Similar to examples describedabove, the augmented reality visualization may comprise the targettrajectory axis 210, the target object 130, the augmented reality window310 and/or the control buttons 320, 322, 324. However, the augmentedreality visualization may further comprise an instrument axis 240. Theinstrument axis 240 may be defined by a line starting at the tip 54 ofthe surgical instrument 50 and extending from the tip 54 along thenormal axis of surgical instrument 50, wherein the normal axis generallybisects the surgical instrument 50. For example, as illustrated in FIG.4, the instrument axis 240 is defined by a line that starts at the tip54 of the surgical instrument 50 and extends generally parallel to alongitudinal axis that bisects the surgical instrument 50. Theinstrument axis 54 may also project beyond the end or tip 54 of thesurgical instrument 50.

The augmented reality visualization illustrated in FIG. 4 furthercomprises an augmented reality position alignment visualization 220. Theaugmented reality position alignment visualization 220 comprises twoaxis-aligned deviation vectors 222, 224 comprising the decomposition ofa distance vector from a point on the target trajectory axis 210 to thetip 54 of the surgical instrument 50, or other portion on the surgicalinstrument 50. Axis-aligned may refer to the line(s) representing thedeviation vector(s) 222, 224 being oriented to be parallel to one of thethree major axes of a reference coordinate system. Typically, the firstdeviation vector 222 may be oriented in parallel to a first axis of thereference coordinate system, and the second deviation vector 224 may beoriented in parallel to a second axis of the reference coordinatesystem. For example, two axis-aligned deviation vectors 222, 224 mayrefer to the line representing the first deviation vector 222 beingoriented to be parallel to the x-axis and the line representing thesecond deviation vector 224 being oriented to be parallel to the y-axisof the reference coordinate system. The reference coordinate system maybe defined relative to the HMD 30, the patient tracker 40, the surgicalinstrument 50, the tracking unit 10, line of sight of the user, or someother point within the surgical field.

The lines representing the first deviation vector 222 and the seconddeviation vector 224 may be configured to intersect at an origin point,wherein the first deviation vector 222 and the second deviation vector224 are positioned to be generally perpendicular to one another. Theorigin of the first deviation vector 222 and the second deviation vector224 may be positioned and/or located on or along the target trajectoryaxis 210. Alternatively, the origin of the first deviation vector 222and the second deviation vector 224 may be positioned and/or locatedproximate the tip 54 of the surgical instrument 50. In yet anotherconfiguration, the origin of the first deviation vector 222 and thesecond deviation vector 224 may be positioned and/or located within theaugmented reality window 310 or floating on the lens 36 of thehead-mounted display 30.

The first deviation vector 222 may be defined by the lateral and/orhorizontal position of the tip 54 of the surgical instrument 50 relativeto the target trajectory axis 210 and/or target object 130. The seconddeviation vector 224 may be defined by the longitudinal and/or verticalposition of the tip 54 of the surgical instrument 50 relative to thetarget trajectory axis 210 and/or target object 130. The size and/orlength of the first deviation vector 222 and/or the second deviationvector 224 may be indicative of the distance or deviation of thesurgical instrument 50 relative to the target trajectory axis 210 in thedirection of the respective deviation vector 222 or 224. For example,the longer the line representing the first deviation vector 222 or thesecond deviation vector 224, the further the surgical instrument 50 maybe positioned from the target trajectory axis 210. Alternatively, theshorter the line representing the first deviation vector 222 or thesecond deviation vector 224, the closer the surgical instrument 50 ispositioned from the target trajectory axis 210. It is also contemplatedthat the lack of a line representing the first deviation vector 222 orthe second deviation vector 224 is indicative that the surgicalinstrument 50 is properly positioned and/or aligned in the directioncorresponding with the absent deviation vector 222, 224. The twoaxis-aligned deviation vectors 222, 224 may assist the user in correctlypositioning and/or aligning the surgical instrument 50 relative to thetarget trajectory axis 210 and/or the target object 130. For example,the two axis-aligned deviation vectors 222, 224 comprising the augmentedreality position alignment visualization 220 are configured to informthe user of the relative location of the surgical instrument 50 relativeto the target trajectory axis 210.

In each of the various configurations of the augmented realityvisualizations, the augmented reality visualizations may be scaled toallow the user to see additional details. The scaling may also allow theuser to see smaller deviations. Referring to FIG. 4, the twoaxis-aligned deviation vectors 222, 224 of the augmented realityposition alignment visualization 220 may be sized and/or scaled to allowthe user to see smaller deviations. For example, the length of the firstdeviation vector 222 and/or the second deviation vector 224 may bescaled by a factor of K, wherein a small deviation of two millimetersbetween the target trajectory axis 210 and the tip 54 of the surgicalinstrument 50 may be represented by a one inch long line representingthe first deviation vector 222 and/or second vector 224 displayed on thelens 36.

In another example, the decomposition of the distance vector into thetwo axis-aligned deviation vectors 222, 224 illustrated in FIG. 4 may bemade based on two eigenvectors derived from: the two of the threeprimary patient axes with the highest angle to the target trajectoryaxis 210, or the line of sight axis being projected onto the planeperpendicular to the target trajectory axis 210 and attached to theclosest point on the target trajectory axis 210 from the tip 54 of thesurgical instrument 54, and the perpendicular vector in the same planeto the projected line of sight axis. The decomposition of the distancevector into two axis-aligned deviation vectors comprising the augmentedreality position alignment visualization 220 may be computed based on totwo eigenvectors. For example, the two eigenvectors may be based on twoof the three primary patient axes of a patient coordinate system withthe highest angle to the target trajectory axis 210. The primary patientaxes of the patient coordinate system may be derived from the patientdata, such as a 3D image data set which was previously registered to thepatient tracker 40. Alternatively, the two eigenvectors may be based ona reference coordinate system defined by the line of sight of the userwith the intention to increase the distinguishability of the firstdeviation vector 222 and/or the second deviation vector 224 as part ofthe augmented reality position alignment visualization 220 for thesurgeon. This may be helpful if the viewing direction of the user isnearly perpendicular to the target trajectory axis 210. The referencecoordinate system may be derived from the plane perpendicular to thetarget trajectory axis 210 and attached to the closest point on thetarget trajectory axis 210 from the tip 54 of the surgical instrument50, and the line of sight of the surgeon. It is also conceivable thatthe two eigenvectors may be based on a combination of both the primarypatient axes of a patient coordinate system and the reference coordinatesystem defined by the line of sight of the user.

In one configuration, the distance between the surgical instrument 50and the target trajectory axis 210 is computed based on the distance ofthe tip 54 of the surgical instrument 50 to at least one locationselected from the group of: a segment connecting the target object 130,230 and an entry point of the target trajectory axis 210, a lineconnecting the target object 130, 230 and the entry point of the targettrajectory axis 210, and the target object 130, 230 or the entry pointof the target trajectory axis 210.

Referring to FIG. 5, another configuration of the augmented realityvisualization from the perspective of the user looking through the lens36 of the HMD 30 is illustrated. As described above, with regard to FIG.4, the augmented reality visualization may comprise the augmentedreality position alignment visualization 220. The augmented realityvisualization may also comprise an augmented reality angular alignmentvisualization 200. The augmented reality angular alignment visualization200 may comprise a deviation angle 206 which represents the anglebetween a first angular vector 204 representative of an axis offset andin parallel with the instrument axis 240 and a second angular vector 202representative of the target trajectory axis 210. For example, theaugmented reality angular alignment visualization 200 is illustrated asa first angular vector 204 representing an axis that is offset and inparallel with the instrument axis 54 of the surgical instrument 50 and asecond angular vector 202 representing the target trajectory axis 210.The first angular vector 204 and the second angular vector 202 may beconnected by an arc representative of the deviation angle 206 betweenthe first angular vector 204 and the second angular vector 202. This mayrepresent the deviation angle 206 between the target trajectory axis 210and the instrument axis 54. As described above, the target trajectoryaxis 210 may be defined by a line connecting a target object 130, 230and an entry point or insertion point proximate to the region ofinterest 62. For example, as illustrated in FIG. 5, the target object230 may comprise image of a screw overlaid on the patient in the plannedposition. This may include an overlaid image of the screw 230 where itis to be inserted into a vertebra of the patient 60. The augmentedreality visualization may further comprise the augmented reality window310, as described above, wherein the augmented reality window 310comprises a label, text, or similar indicia identifying the deviationangle 206 between the first angular vector 204 and the second angularvector 202. For example, the augmented reality window 310 may bepositioned proximate to the augmented reality angular alignmentvisualization 200 and configured to display a text label identifying thedeviation angle 206. The text label displayed in the augmented realitywindow 310 may include “30 Degrees”, “1 Radian”, or similar angularmeasurement.

In another example, the visualization of the deviation angle 206comprises: a position corrected augmented reality visualization of theinstrument axis 240, the target trajectory axis 210 and an arcconnecting proximal ends of both the instrument axis 240 and the targettrajectory axis 210, or an axonometry of the position correctedaugmented reality visualization. Axonometry is a graphical procedurebelonging to descriptive geometry that generates a planar image of athree-dimensional object. The term “axonometry” can be defined as “tomeasure along axes”, and may indicate that the dimensions and scaling ofthe coordinate axes are important. The result of an axonometricprocedure is a uniformly-scaled parallel projection of the object.

In the example configuration illustrated in FIG. 5, the target object230 comprises an augmented reality visualization of the planned locationfor a screw to be inserted in a vertebra of the patient 60, and thesecond angular vector 202 is representative of the orientation of thetarget trajectory axis 210 for inserting the screw in the identifiedlocation. The augmented reality visualization of the target object 230raises spatial awareness when in situations where the real surgicaltarget is hidden from the surgeon's view. Furthermore, the arcrepresenting the deviation 206 connecting the first angular vector 204representing the instrument axis 240 of the surgical instrument 50relative to the target object 230 and the second angular vector 202representing the target trajectory axis 210 provides a visual cue to theuser of an approximation for correcting the deviation of the angle 206between the first angular vector 204 and second angular vector 202.

The augmented reality angular alignment visualization 200 may also bescaled to allow the user to more easily see smaller deviations in thedeviation angle 206. For example, as illustrated in FIG. 5, the lengthof the line representing the first angular vector 204 and/or the lengthof the line representing the second angular vector 202 may be scaled bya factor of K to exaggerate the line representing the first angularvector 204 and the second angular vector 202 to allow the user to moreeasily see smaller deviations in the deviation angle 206 represented bythe arc. The scaling of the length of the line representing the firstangular vector 204 and/or the length of the line representing the secondangular vector 202 is typically chosen that the visualized length of thefirst angular vector 204 and/or the length of the line representing thesecond angular vector 202 corresponds to several centimeters. In case ofadditional visualization of the target object 130, 230, such as apedicle screw, the length of the line representing the first angularvectors 204 and/or the second angular vector 202 may also depend on thelength/size of this target object 130, 230. Scaling may also includescaling the line representing the first angular vector 204 and/or theline representing the second angular vector 202 to increase the lengthof the line representing the first angular vector 204 and/or the linerepresenting the second angular vector 202. Alternatively, this may alsoinclude scaling the line representing the first angular vector 204and/or the line representing the second angular vector 202 to decreasethe length of the line representing the first angular vector 204 and/orthe line representing the second angular vector 202 to reduce the sizeof the augmented reality angular alignment visualization 200 on the lens36. This may prevent the augmented reality angular alignmentvisualization 200 from obstructing or interfering with the user's view.

In another example, the decomposition of the deviation angle 206 may bescaled relative to the two eigenvectors derived from: the two of thethree primary patient axes with the highest angle to the targettrajectory axis 210, or the line of sight axis being projected onto theplane perpendicular to the target trajectory axis 210 and attached tothe closest point on the target trajectory axis 210 from the tip 54 ofthe surgical instrument 50, and the perpendicular vector in the sameplane to the projected line of sight axis. As described above, the twoeigenvectors may be based on two of the three primary patient axes of apatient coordinate system with the highest angle to the targettrajectory axis 210. Alternatively, the two eigenvectors may be based ona reference coordinate system defined by the line of sight of the userwith the intention to increase the distinguishability of the firstdeviation vector 222 and/or the second deviation vector 224 as part ofthe augmented reality position alignment visualization 220 for thesurgeon. This may be helpful if the viewing direction of the user isnearly perpendicular to the target trajectory axis 210.

Furthermore, it should be understood that the various configurations ofthe augmented reality visualizations described above may includehighlighting and/or color schemes to allow the user to distinguishbetween the various types of augmented reality visualizations. Forexample, augmented reality position alignment visualization 220 may bedisplayed on the lens 36 of the HMD 30 in a first color, and theaugmented reality angular alignment visualization 200 may be displayedon the lens 36 of the HMD 30 in a second color. The first color and thesecond color may be selected to be distinguishable from one another. Thedistinguishable and/or different colors for the various features orelements of the augmented reality visualizations may be selected from abase color of a trajectory by equidistant placing of alternate colors ina chromaticity space around a white point and selecting their dominantwavelength by extrapolation. The colors may be selected fromhigh-luminance complementary colors selected from the group comprisingyellow, pink, green and cyan. Referring back to FIG. 5, in anon-limiting example, the first deviation vector 222 and the seconddeviation vector 224 of augmented reality position alignmentvisualization 220 may be displayed on the lens 36 of the HMD 30 aspurple colored lines. By contrast, the first angular vector 204 and thesecond angular vector 202 of augmented reality angular alignmentvisualization 200 may be displayed on the lens 36 of the HMD 30 as blueor cyan colored lines. A different color may similarly be used todistinguish the target trajectory axis 210 from the other visualization.For example, the target trajectory axis 210 may be displayed on the lens36 of the HMD 30 as a yellow colored line. It should be understood thatit is contemplated that any combination of colors may be utilized foreach of the various augmented reality visualizations to distinguish themfrom one another.

The augmented reality visualization described above may also bedistinguishable as displayed on the lens 36 of the HMD 30 by varying thetransparency and/or opacity of each augmented reality visualization. Forexample, augmented reality visualization may be configured such that theaugmented reality position alignment visualization 220 may be displayedon the lens 36 of the HMD 30 with opaque lines, and the augmentedreality angular alignment visualization 200 may be displayed on the lens36 of the HMD 30 as an at least partially transparent line or completelyhidden from view. In another example, wherein the augmented realityvisualization comprises a plurality of trajectories and/or axes, alltrajectories and/or axes except the one with the minimum distance fromthe instrument axis 240 and/or the tip 54 of the surgical instrument 50may be displayed with increased transparency. This eliminatesunnecessary or less important augmented reality visualizations from theview of the user.

The line type may similarly be utilized to distinguish the variousaugmented reality visualizations described above. Referring back to FIG.5, in a non-limiting example, the first deviation vector 222 and thesecond deviation vector 224 of augmented reality position alignmentvisualization 220 may be displayed on the lens 36 of the HMD 30 as asolid line having a defined line weight. By contrast, the first angularvector 204 and the second angular vector 202 of augmented realityangular alignment visualization 200 may be displayed on the lens 36 ofthe HMD 30 as a solid line having a line weight that is different fromthe line weight of the augmented reality position alignmentvisualization 220. A different line type may similarly be used todistinguish the target trajectory axis 210 from the other visualization.For example, the target trajectory axis 210 may be displayed on the lens36 of the HMD 30 as a dashed, dotted, or similarly distinct line type.It should be understood that is it contemplated that any combination ofline types may be utilized for each of the various augmented realityvisualizations to distinguish them from one another.

FIG. 6 illustrates an example configuration of the augmented realityvisualization comprising only a virtual image as perceived by the userthrough the lens 36 of the HMD 30. As illustrated in FIG. 6, theaugmented reality visualization may comprise a virtual image of a sliceof the patient image data shown in a fixed position floating frame 300above the real surgical site or region of interest 62 as viewed throughthe lens 36. Similar to examples described above, the user may stillview the real features of the patient 60, such as the patient's 60spine, through the lens 36 of the HMD 30. However, additionalinformation or images, such as patient data, may be displayed in afloating frame 300 on the lens 36. For example, as illustrated in FIG.6, the augmented reality visualization may comprise an image of a sliceof the patient data, such as a two-dimensional image of a specificvertebra. An axis or coordinate system may be overlaid on the slice ofthe patient data depicted in the floating frame 300. The axis orcoordinate system may be configured to represent the position and/ororientation of the surgical instrument 50 relative to the patient datadepicted in the floating frame 300.

Referring to FIG. 7, in another example configuration of the augmentedreality visualization, the augmented reality visualization may comprisea virtual image that is displayed on the lens 36 of the HMD 30 in adisplay window 330. Different from some of the prior exampleconfigurations of augmented reality visualizations described above, theaugmented reality visualization illustrated in FIG. 7 is an example ofan augmented reality visualization comprising only a virtual imagedisplayed on the lens 36. For example, the augmented realityvisualization does not require the user of the HMD 30 to be in view ofthe patient 60 and/or the region of interest 62. This augmented realityvisualization may be displayed on the lens 36 to allow the user to viewan image or depiction of the surgical plan overlaid on a virtual imageor model of the patient 260. Similar to the floating frame 300 describedabove, the display window 330 may be configured to depict patient data,such as an image or patient scan. The display window 330 may be furtherconfigured to depict the target trajectory axis 210, the instrument axis240, and/or the target object 130 overlaid on the patient data. As insimilar examples described above, the display window 330 of thisaugmented reality visualization may be manipulated by the user usingcontrol button(s) 320, 322, 324. For example, the user may use a handgesture to select one or more of the control button(s) 320, 322, 324 tozoom-in or zoom-out to get a better visual of the target trajectory axis210, the instrument axis 240, and/or the target object 130.

FIG. 8 illustrates another alternative configuration of the augmentedreality visualization including a virtual image of a portion of thepatient 260 and/or patient data as displayed on the lens 36 of the HMD30. The portion of the patient 260 and/or patient data displayed on thelens 36 as the augmented reality visualization may include the targettrajectory axis 210, region of interest 262, and/or the target object130. The augmented reality visualization may also comprise a depictionof additional anatomical features and/or a planned surgical pathwayoverlaid on the patient 260 and/or patient data. For example, theaugmented reality visualization may comprise a virtual 3-D image of thepatient 260 displayed on the lens 36. This may allow the user tovisualize the additional anatomical features and/or the planned surgicalpathway on the lens 36 of the HMD 30, as opposed to having to diverttheir attention to another external display. The augmented realityvisualization may further comprise additional control buttons 326, 328,wherein the control buttons 326, 328 are configured to manipulate theaugmented reality visualization displayed on the lens 36. For example,one of the control buttons 326, 328 may be configured to zoom-in and/orzoom-out. Additionally, one of the control buttons 326, 328 may beconfigured to rotate the augmented reality visualization to allow theuser to observe or view the augmented reality visualization from adifferent angle or perspective. When the augmented reality visualizationis a virtual 3-D image of the patient 260, the control buttons 326, 328may be configured to rotate the virtual 3-D model of the patient 260 toallow the user to view the surgical plan and/or target trajectory axis210 from multiple angles.

A method of aligning the surgical instrument 50 using the surgicalnavigation system 20 including the head-mounted display 30 describedabove may comprise planning the target trajectory axis 210 based onpatient data registered to the patient tracker 40. The method mayfurther comprise the step of displaying on the head-mounted display 30the augmented reality position alignment visualization 220 as twoaxis-aligned deviation vectors 222, 224 comprising the decomposition ofa distance vector from a point on the target trajectory axis 210 to atip 54 of the surgical instrument 50. For example, the method maycomprise displaying the first deviation vector 222 and the seconddeviation vector 224 on the lens 36 of the head-mounted display 30. Thefirst deviation vector 222 and/or the second deviation vector 224 may bedisplayed as a solid and/or a dotted line. The first deviation vector222 and the second deviation vector 224 may also be displayed as anarrow.

The method may further comprise the step of displaying on thehead-mounted display 30 the augmented reality angular alignmentvisualization 200 comprising the deviation angle 206 which shows theangle between the first angular vector 204 representative of theinstrument axis 240 of the surgical instrument 50 and the second angularvector 202 of the target trajectory axis 210. For example, the methodmay comprise displaying the first angular vector 204 and the secondangular vector 202 as lines connected by an arc representative of thedeviation angle 206 between the first angular vector 204 and the secondangular vector 202.

The method may also comprise the step of updating the augmented realityposition alignment visualization 220 and/or the augmented realityangular alignment visualization 200 displayed on the head-mounteddisplay 30 based on the measurement data of the tracking unit 10 toindicate the relative location of the surgical instrument 50 to thetarget trajectory axis 210 from the perspectives of the head-mounteddisplay 30. The target trajectory axis 210 may be defined by a lineconnecting the target object 130, 230 and an entry point. This updatingmay be continuous.

The method of aligning the surgical instrument 50 may further comprisedisplaying the augmented reality visualization of the instrument axis240 of the surgical instrument 50. The instrument axis 240 may bedisplayed as line or an outline of the surgical instrument 50. Theaugmented reality visualization of the instrument axis 240 displayed onthe lens 36 of the head-mounted display 30 may indicate the position ofthe surgical instrument 50 relative to the patient 60, the region ofinterest 62, the target trajectory axis 210, and/or the target object130, 230.

The method of aligning the surgical instrument 50 may further compriseusing different colors for displaying the augmented reality positionalignment visualization 220 and/or the augmented reality angularalignment visualization 200 so that the user can distinguish therespective alignment visualizations. The different colors for theaugmented reality visualizations may be selected from a base color of atrajectory by equidistant placing of alternate colors in a chromaticityspace around a white point and selecting their dominant wavelength byextrapolation. For example, the colors may be selected fromhigh-luminance complementary colors selected from the group comprisingyellow, pink, green and cyan.

The method may also comprise highlighting the augmented reality positionalignment visualization 220 and/or the augmented reality angularalignment visualization 200 to the user based on the distance of thesurgical instrument 50 to the target trajectory axis 210. For example,the color and or the line weight of the lines representing the augmentedreality position alignment visualization 220 may be different from thecolor and or the line weight of the lines representing the augmentedreality angular alignment visualization 200. As described above, thismay be utilized to allow the user to distinguish between the augmentedreality position alignment visualization 220 and/or the augmentedreality angular alignment visualization 200 displayed on the lens 36 ofthe head-mounted display 30.

The step of highlighting of the target trajectory axis 210 may furthercomprise the step of hiding all additional trajectories from the userexcept the one with the minimum distance. The step of highlighting thetarget trajectory axis 210 may also comprise showing all additionaltrajectories except the one with the minimum distance with increasedtransparency. For example, when the surgical instrument 50 is properlyaligned with the direction and orientation corresponding to the firstdeviation vector 222 of the augmented reality position alignmentvisualization 220, the first deviation vector 222 may be hidden ordisplayed as transparent on the lens 36 of the head-mounted display 30.By contrast, if the surgical instrument 50 is misaligned with thedirection and orientation corresponding to the first deviation vector222 of the augmented reality position alignment visualization 220, thefirst deviation vector 222 may be highlighted on the lens 36 of thehead-mounted display 30 to signal to the user that a correction in thealignment is needed based on the target trajectory axis 210.

The method of aligning the surgical instrument 50 may further comprisethe step of displaying on the head-mounted display 30 the augmentedreality position alignment visualization 220 as two axis-aligneddeviation vectors 222, 224 wherein the distance between the surgicalinstrument 50 and the target trajectory axis 210 is computed based onthe distance of the tip 54 of the surgical instrument 50 to at least oneselected from the group consisting of a segment connecting the targetobject 130, 230 and an entry point of the target trajectory axis 210, aline connecting the target object 130, 230 and the entry point of thetarget trajectory axis 210, and the target object 130, 230 or the entrypoint of the target trajectory axis 210.

The method of aligning the surgical instrument 50 wherein thedecomposition of the distance vector into two axis-aligned deviationvectors 222, 224 is relative to two eigenvectors derived from: two ofthe three primary patient axes with the highest angle to the targettrajectory axis 210, or a line of sight axis being projected onto aplane perpendicular to the target trajectory axis 210 and attached tothe closest point on the target trajectory axis 210 from the tip 54 ofthe surgical instrument 50, and a perpendicular vector in the same planeto the projected line of sight axis.

The method of aligning the surgical instrument 50 may further comprisethe step of scaling the augmented reality position alignmentvisualization 220 to allow the user to more easily observe smalldeviations in the position and/or alignment of the surgical instrument50 relative to the target trajectory axis 210. For example, the lengthof the first deviation vector 222 and/or the second deviation vector 224may be scaled up to allow the user to more easily observe smalldeviations. Alternatively, the length of the first deviation vector 222and/or the second deviation vector 224 may be scaled down to allow theaugmented reality visualization to fit on the lens 36 of thehead-mounted display 30. The scaling of the decomposition of thedistance vector may be limited to an absolute maximum visualized lengthand a maximum visualized length in relation to a field of view of thehead-mounted display 30.

The method of aligning the surgical instrument 50 wherein thedecomposition of the deviation angle 206 is relative to two eigenvectorsderived from: two of the three primary patient axes with the highestangle to the target trajectory axis, or a line of sight axis beingprojected onto a plane perpendicular to the target trajectory axis andattached to the closest point on the target trajectory axis from the tip54 of the surgical instrument 50, and a perpendicular vector in the sameplane to the projected line of sight axis.

The method of aligning the surgical instrument 50 wherein thevisualization of the deviation angle 206 comprises: a position correctaugmented reality visualization of the instrument axis 240, the targettrajectory axis 210 and an arc representing the deviation angle 206connecting proximal ends of both the first angular vector 204representing the instrument axis 240 and the second angular vector 202representing the target trajectory axis 210, or an axonometry of theposition correct augmented reality visualization.

The method of aligning the surgical instrument 50 may further comprisethe step of displaying a first augmented reality textual label 310 fordescribing the distance from the tip 54 of the surgical instrument 50 tothe target trajectory axis 210 and a second augmented reality textuallabel 310 for describing the deviation angle 206 in degrees between theinstrument axis 240 and the target trajectory axis 210 positioned in ornear the angular visualization.

The method of aligning the surgical instrument 50 may further comprisethe step of displaying an augmented reality visualization of the targetobject 130, 230 to be placed or removed at a target point of the targettrajectory axis 210.

The method of aligning the surgical instrument 50 may further comprisethe step of displaying the augmented reality visualization of the targetobject 130, 230 to be placed or removed at a target point of the targettrajectory axis 210 wherein the augmented reality visualization of thetarget object 130, 230 is positioned at the target position or at thecurrent position of the surgical instrument 50.

The method of aligning the surgical instrument 50 may further comprisethe step of displaying an augmented reality visualization of a slice ofpatient image data. This step may comprise selecting an augmentedreality visualization location chosen by the user to be one of a fixedframe in space, a floating frame 300 following head movement, anin-place at the position of the patient image data slice, or an offsetfrom the patient position by a user defined fixed spatial vector. Theuser may manipulate the slice of the patient image data using controlbuttons 320, 322, 324, 326, 328 displayed on the lens 36 of thehead-mounted display 30. The user may select the control buttons 320,322, 324, 326, 328 displayed on the lens 36 using hand and/or facialgestures. This step may further comprise color mapping from patientimage data color information to augmented reality visualization colorinformation including alpha transparency target ranges. The step mayfurther comprise a user interaction by which the user can use any ofvoice, mouse, keyboard, gaze, or surgical instruments to choose andreposition the augmented reality visualization location and select theslice of patient image data.

The method of aligning the surgical instrument 50 may further comprisedisplaying a region of interest indicator. The region of interestindicator may comprise an augmented reality textual label 310 shown inthe vicinity of the region of interest 62 or an augmented realityboundary visualization demarcating the region of interest 62. The regionof interest indicator may further comprise a color mapping method whichhighlights to the user the augmented reality textual labels 310 andaugmented reality boundary visualization based on the distance of thesurgical instrument 50 to the region of interest 62.

Several configurations of augmented reality visualizations, such as theaugmented reality position alignment visualization 220 and/or theaugmented reality angular alignment visualization 200, are describedabove. While many of the configurations of the augmented realityvisualization are described with regard to being displayed on a lens 36of a head-mounted display 30 and/or on the head-mounted display 30, itshould be understood that it is also contemplated that any of thevarious configurations of the augmented reality visualizations may alsobe display on a display 22. The display 22 may comprise a cathode raytube display (CRT), light-emitting diode display (LED),electroluminescent display (ELD), liquid crystal display (LCD), organiclight-emitting diode display (OLED), digital light processing display(DLP), projection monitor, or similar device.

Several configurations of a surgical navigation system 20 and/or anaugmented reality visualization have been discussed in the foregoingdescription. However, the configurations discussed herein are notintended to be exhaustive or limit the disclosure to any particularform. The terminology which has been used is intended to be in thenature of words of description rather than of limitation. Manymodifications and variations are possible in light of the aboveteachings and the disclosure may be practiced otherwise than asspecifically described.

CLAUSES FOR ADDITIONAL CONFIGURATIONS (ORIGINAL EP CLAIMS)

I. A guidance system for the alignment of a surgical instrumentcomprising a stereoscopic head-mounted display comprising at least a HMDtracker, a surgical navigation system with tracking system, patient dataregistered to a patient tracker trackable by the tracking system, aplanning system for planning one or more trajectories on the patientdata, a navigated instrument tracked by the tracking system, a ARposition alignment visualization, an AR angular alignment visualization.

I-a. The guidance system of clause I may be configured to display twoaxis-aligned deviation vectors for the position alignment visualizationwhich are the decomposition of the distance vector from the nearestpoint on the trajectory axis of the tip of the navigated instrument tothe tip of the navigated instrument and which are scaled in length by ascaling function to allow the user to see small deviations on thestereoscopic head-mounted display.

I-b. The guidance system of clause I or I-a may further be configured todisplay the angular alignment visualization consisting of one or twodeviation angles which show the angle between the direction vector ofthe axis of the instrument and the direction vector of the trajectoryaxis or the decomposition of said angle into two deviation angles andeach of which might are scaled in opening angle by a scaling function toallow the user to see small deviations.

I-c. The guidance system of any of clauses I, I-a, and I-b may furtherbe configured to update the visualizations continuously based on thetracking system to show the relative location of the navigatedinstrument to the patient data from the perspectives of the both eyes ofthe stereoscopic head-mounted display.

I-d. The guidance system of any of clauses I, I-a, I-b, and I-c mayfurther be configured to use different colors for the visualizations sothat the user can distinguish the respective alignment visualizationsand to highlight the visualizations to the user based on the distance ofthe navigated instrument to each trajectory.

II. A method for the alignment of a surgical instrument using a guidancesystem of clause I, the method comprising the steps of: updating thevisualizations continuously based on the tracking system to show therelative location of the navigated instrument to the patient data fromthe perspectives of the both eyes of the stereoscopic HMD; usingdifferent colors for the visualizations so that the user can distinguishthe respective alignment visualizations; and highlighting thevisualizations to the user based on the distance of the navigatedinstrument to each trajectory.

II-a. The method according to clause II may further comprise usingand/or displaying two axis-aligned deviation vectors for the positionalignment visualization which are the decomposition of the distancevector from the nearest point on the trajectory axis of the tip of thenavigated instrument to the tip of the navigated instrument and whichare scaled in length by a scaling function to allow the user to seesmall deviations.

II-b. The method according to clauses II or II-a may further compriseusing and/or displaying the angular alignment visualization consistingof one or two deviation angles which show the angle between thedirection vector of the axis of the instrument and the direction vectorof the trajectory axis or the decomposition of said angle into twodeviation angles and each of which might are scaled in opening angle bya scaling function to allow the user to see small deviations.

II-c. The method according to any of clauses II, II-a, and II-b,characterized in that the distance between the navigated instrument andthe trajectory is computed based on the distance of either the tip ofthe navigated instrument to at least one selected from the groupconsisting of the segment connecting target and entry point of thetrajectory, the line connecting target and entry point of thetrajectory, and target or entry point of the trajectory.

II-d. The method according to any of clauses II, II-a, and II-b,characterized in that the angular deviation between the navigatedinstrument and the trajectory is computed based on the angle between thenormal of the axis of the navigated instrument and the normal of theline connecting target and entry point of the trajectory.

II-e. The method according to any of clauses II, II-a, and II-b,characterized in that the highlighting of trajectories hides alltrajectories from the user except the one with the minimum distance andshows all trajectories except the one with the minimum distance withincreased transparency.

II-f. The method according to any of clauses II, II-a, and II-b,characterized in that the decomposition of the distance vector in twoaxis-aligned deviation vectors is relative to the two eigenvectorsderived from: the two of the three primary patient axes with the highestangle to the trajectory axis, or the line of sight axis being projectedonto the plane perpendicular to the trajectory axis and attached to theclosest point on the trajectory axis from the tip of the navigatedinstrument, and the perpendicular vector in the same plane to theprojected line of sight axis.

II-g. The method according to any of clauses II, II-a, and II-b,characterized in that the scaling of the decomposition of the distancevector is limited to an absolute maximum visualized length and a maximumvisualized length in relation to the field of view of the head-mounteddisplay.

II-h. The method according to any of clauses II, II-a, and II-b,characterized in that the decomposition of the two deviation angles isrelative to the two eigenvectors derived from: the two of the threeprimary patient axes with the highest angle to the trajectory axis, orthe line of sight axis being projected onto the plane perpendicular tothe trajectory axis and attached to the 5 closest point on thetrajectory axis from the tip of the navigated instrument, and theperpendicular vector in the same plane to the projected line of sightaxis.

II-i. The method according to any of clauses II, II-a, and II-b,characterized in that the visualization of a deviation angle consistsof: a position correct augmented reality visualization of the currentnormal axis, the target normal axis and the arc connecting the proximalends of both current and target normal axis, or an axonometry of theposition correct augmented reality visualization.

II-j. The method according to any of clauses II, II-a, and II-b, furtherusing an AR textual label for describing the distance from theinstrument tip to the trajectory target and an AR textual label fordescribing the angular deviation in degrees between the instrument axisand the trajectory axis positioned in or near the angular visualization.

II-k. The method according to any of clauses II, II-a, and II-b, furtherusing an AR visualization of the trajectory.

II-l. The method according to any of clauses II, II-a, and II-b, furtherusing an AR visualization of the target object to be placed or removedat the target point of the trajectory characterized in that the ARvisualization of the target object is positioned at the target positionor at the current position of the navigated tool.

II-m. The method according to any of clauses II, II-a, and II-b, furthercomprising the step of an AR visualization of the target object to beplaced or removed at the target point of the trajectory.

II-n. The method according to any of clauses II, II-a, and II-b,characterized in that the different colours for the visualization areselected from a base colour of a trajectory by equidistant placing ofalternate colours in a chromaticity space around the white point andselecting their dominant wavelength by extrapolation or that the coloursare selected from high-luminance complementary colours selected from thegroup comprising yellow, pink, green and cyan.

II-o. The method according to any of clauses II, II-a, and II-b, furthercomprising the step of an AR visualization of a slice of patient imagedata comprising the steps of: a AR visualization location chosen by thesurgeon to be one of fixed frame in space, floating frame following headmovement, in-place at the position of the patient image data slice oroffset from the patient position by a user defined fixed spatial vector;a color mapping from patient image data color information to ARvisualization color information including alpha transparency targetranges; and a user interaction by which the user can use any of voice,mouse, keyboard, gaze, or navigated surgical instruments to choose andreposition the AR visualization location and select the slice of patientimage data.

II-p. The method according to any of clauses II, II-a, and II-b, furthercomprising the use of a region of interest indicator comprising: a ARtextual labels shown in the vicinity of the region of interests or a ARboundary visualizations demarcating the region of interests, and a colormapping method which highlights to the user the AR textual labels and ARboundary visualization based on the distance of the navigated instrumentto the region of interest.

CLAUSES FOR ADDITIONAL CONFIGURATIONS (ORIGINAL PCT CLAIMS)

III. A head-mounted display for use with surgical navigation systemincluding a patient tracker and a surgical instrument tracker, thesurgical navigation system configured to plan a target trajectory axisbased on patient data and for the alignment of an instrument axis thatis at least partially defined by a tip of a surgical instrument with thetarget trajectory axis, said head-mounted display comprising:

a lens; and

wherein the head-mounted display is configured to display an augmentedreality position alignment visualization comprising two axis-aligneddeviation vectors comprising the decomposition of a distance vector froma point on the target trajectory axis to the tip of the surgicalinstrument; and/or

wherein the head-mounted display is further configured to display anaugmented reality angular alignment visualization comprising a deviationangle which represent the angle between a first angular vectorrepresentative of the instrument axis and a second angular vectorrepresentative of the target trajectory axis.

III-a. The head-mounted display of clause III, wherein the twoaxis-aligned deviation vectors are configured to be scaled in length toallow the user to see small deviations in the distance from the surgicalinstrument axis to the target trajectory axis.

III-b. The head-mounted display of clause III, wherein the deviationangle is configured to be scaled to allow the user to see smalldeviations in the angle between the first angular vector and the secondangular vector.

III-c. The head-mounted display of clause III, wherein the augmentedreality angular alignment visualization comprises a decomposition of theangle between a first angular vector representative of the instrumentaxis and a second angular vector representative of the target trajectoryaxis of the angle into two deviation angles.

III-d. The head-mounted display of clause III, wherein the augmentedreality position alignment visualization comprises a first color and theaugmented reality angular alignment visualization comprises a secondcolor; and

wherein the first color is distinguishable from the second color.

IV. A method of aligning a surgical instrument using a surgicalnavigation system, the surgical navigation system including a trackingunit configured to track the position of a head-mounted display, apatient tracker, and a surgical instrument tracker coupled to a surgicalinstrument having a tip and defines an instrument axis, and wherein thesurgical navigation system is configured to plan a target trajectoryaxis based on patient data registered to the patient tracker, the methodcomprising the steps of:

displaying on the head-mounted display an augmented reality positionalignment visualization as two axis-aligned deviation vectors comprisingthe decomposition of a distance vector from a point on the targettrajectory axis to the tip of the surgical instrument, and/or

displaying on the head-mounted display an augmented reality angularalignment visualization comprising a deviation angle which shows theangle between a first angular vector representative of the surgicalinstrument axis and a second angular vector representative of the targettrajectory axis; and

continuously updating the augmented reality position alignmentvisualization and/or the augmented reality angular alignmentvisualization displayed on the head-mounted display based on thetracking unit to indicate the location of the surgical instrument axisrelative to the target trajectory axis from the perspectives of thehead-mounted display.

IV-a. The method according to clause IV, wherein the target trajectoryaxis defined by a line connecting a target object and an entry point.

IV-b. The method according to clauses IV or IV-a, further comprisingdisplaying an augmented reality visualization of an instrument axis ofthe surgical instrument on the head-mounted display.

IV-c. The method according to clause IV, further comprising usingdifferent colors for displaying the augmented reality position alignmentvisualization and/or the augmented reality angular alignmentvisualization so that the user can distinguish the respective alignmentvisualization; and

highlighting the augmented reality position alignment visualizationand/or the augmented reality angular alignment visualization to the userbased on the distance of the surgical instrument to the targettrajectory axis.

IV-d. The method according to clause IV, wherein the distance betweenthe surgical instrument and the target trajectory axis is computed basedon the distance of the tip of the surgical instrument to at least oneselected from the group consisting of a segment connecting a targetobject and an entry point of the target trajectory axis, a lineconnecting the target object and the entry point of the targettrajectory axis, the target object, and the entry point of thetrajectory.

IV-e. The method according to clause IV-c, wherein the highlighting ofthe target trajectory axis comprises hiding all additional trajectoriesfrom the user except the one with the minimum distance.

IV-f. The method according to clause IV-c, showing all additionaltrajectories except the one with the minimum distance with increasedtransparency.

IV-g. The method according to clause IV, wherein the decomposition ofthe distance vector into two axis-aligned deviation vectors is relativeto two eigenvectors derived from:

two of the three primary patient axes with the highest angle to thetarget trajectory axis, and

a line of sight axis being projected onto a plane perpendicular to thetarget trajectory axis and attached to the closest point on the targettrajectory axis from the tip of the surgical instrument, and aperpendicular vector in the same plane to the projected line of sightaxis.

IV-h. The method according to clause IV, further comprising scaling theaugmented reality position alignment visualization;

wherein the scaling of the decomposition of the distance vector islimited to an absolute maximum visualized length and a maximumvisualized length in relation to a field of view of the head-mounteddisplay.

IV-i. The method according to clause IV, wherein the decomposition ofthe two deviation angles is relative to two eigenvectors derived from:

two of the three primary patient axes with the highest angle to thetarget trajectory axis, and

a line of sight axis being projected onto a plane perpendicular to thetarget trajectory axis and attached to the closest point on the targettrajectory axis from the tip of the surgical instrument, and aperpendicular vector in the same plane to the projected line of sightaxis.

IV-j. The method according to clause IV-c, wherein the visualization ofthe deviation angle comprises:

a position correct augmented reality visualization of the instrumentaxis, the target trajectory axis and an arc connecting proximal ends ofboth the instrument axis and the target trajectory axis.

IV-k. The method according to clause IV-c, wherein the visualization ofthe deviation angle comprises:

an axonometry of a position correct augmented reality visualization ofthe instrument axis.

IV-l. The method according to clause IV-b, further comprising displayinga first augmented reality textual label for describing the distance fromthe tip of the surgical instrument to the target trajectory axis and asecond augmented reality textual label for describing the deviationangle in degrees between the instrument axis and the target trajectoryaxis positioned in or near the angular visualization.

IV-m. The method according to clause IV, further comprising displayingan augmented reality visualization of a target object to be placed orremoved at a target point of the target trajectory axis wherein theaugmented reality visualization of the target object is positioned atthe target position or at the current position of the surgicalinstrument.

IV-n. The method according to clause IV, further comprising the step ofan augmented reality visualization of a target object to be placed orremoved at a target point of the target trajectory axis.

IV-o. The method according to clause IV-a, wherein the different colorsfor the augmented reality visualizations are selected from a base colorof a trajectory by equidistant placing of alternate colors in achromaticity space around a white point and selecting their dominantwavelength by extrapolation; and/or

wherein the colors are selected from high-luminance complementary colorsselected from the group comprising yellow, pink, green and cyan.

IV-p. The method according to clause IV, further comprising the step ofdisplaying an augmented reality visualization of a slice of patientimage data comprising the steps of:

selecting an augmented reality visualization location chosen by thesurgeon to be one of a fixed frame in space, a floating frame followinghead movement, an in-place at the position of the patient image dataslice, or an offset from the patient position by a user defined fixedspatial vector;

a color mapping from patient image data color information to augmentedreality visualization color information including alpha transparencytarget ranges; and

a user interaction by which the user can use any of voice, mouse,keyboard, gaze, or surgical instruments to choose and reposition theaugmented reality visualization location and select the slice of patientimage data.

IV-q. The method according to clause IV, further comprising displaying aregion of interest indicator, said region of interest indicatorcomprising:

an augmented reality textual labels shown in the vicinity of the regionof interests or

an augmented reality boundary visualizations demarcating the region ofinterests, and

a color mapping method which highlights to the user the augmentedreality textual labels and augmented reality boundary visualizationbased on the distance of the navigated instrument to the region ofinterest.

V. A surgical navigation system, a patient tracker trackable by thesurgical navigation system, and a surgical instrument trackable by thesurgical navigation system, said surgical instrument guidance systemcomprising:

a display;

a controller configured to display an augmented reality positionalignment visualization on the display as two axis-aligned deviationvectors comprising a decomposition of a distance vector from a targetpoint on a target trajectory axis to the surgical instrument on saiddisplay; and/or

wherein the controller is further configured to display an augmentedreality angular alignment visualization on the display comprising adeviation angle which represent the angle between a first angular vectorrepresentative of the instrument axis and a second angular vectorrepresentative of the target trajectory axis.

1. A surgical navigation system comprising: a head-mounted displaycomprising a lens; a surgical navigation system comprising a trackingunit; a patient tracker registered to patient data and trackable by saidsurgical navigation system; a surgical instrument having an instrumenttracker trackable by said surgical navigation system, said instrumentdefines an instrument axis; and a controller configured to generate anaugmented reality position alignment visualization as two axis-aligneddeviation vectors comprising the decomposition of a distance vector froma target point on a target trajectory axis to a point on the surgicalinstrument to display on said lens of said head-mounted display.
 2. Thesurgical navigation system of claim 1, wherein the controller isconfigured to scale the two axis-aligned deviation vectors displayed onsaid lens.
 3. The surgical navigation system of claim 1, wherein thecontroller is configured to generate an augmented reality angularalignment visualization to display on the lens.
 4. The surgicalnavigation system of claim 3, wherein the augmented reality angularalignment visualization comprises a deviation angle which represents theangle between a first angular vector representative of an axis parallelto the instrument axis and a second angular vector representative of thetarget trajectory axis.
 5. The surgical navigation system of claim 4,wherein the controller is configured to scale the length of a first lineand a second line representing the deviation angle to allow the user tosee small deviations in the deviation angle.
 6. The surgical navigationsystem of claim 3, wherein the augmented reality angular alignmentvisualization comprises a decomposition of the angle between a firstangular vector representative of the instrument axis and a secondangular vector representative of the target trajectory axis into twodeviation angles.
 7. The surgical navigation system of claim 6, whereinthe length of lines representing the two deviation angles are configuredto be scaled to allow the user to see small deviations in the twodeviation angles.
 8. The surgical navigation system of claim 3, whereinthe augmented reality position alignment visualization comprises a firstcolor and the augmented reality angular alignment visualizationcomprises a different color that is distinguishable from the firstcolor.
 9. A head-mounted display system for use with a surgicalnavigation system, a patient tracker trackable by the surgicalnavigation system, and a surgical instrument trackable by the surgicalnavigation system, said head-mounted display system comprising: a lens;and a controller configured to display an augmented reality positionalignment visualization as two axis-aligned deviation vectors comprisinga decomposition of a distance vector from a target point on a targettrajectory axis to the surgical instrument on said lens.
 10. Thehead-mounted display system of claim 9, wherein the controller isconfigured to generate an augmented reality angular alignmentvisualization on said lens.
 11. The head-mounted display system of claim10, wherein the augmented reality angular alignment visualizationcomprises a deviation angle which represent the angle between a firstangular vector representative of the instrument axis and a secondangular vector representative of the target trajectory axis, the lengthof a first line and a second line representing the deviation angle isconfigured to be scaled to allow the user to see small deviations. 12.The head-mounted display system of claim 10, wherein the augmentedreality angular alignment visualization comprises a decomposition of theangle between a first angular vector representative of the instrumentaxis and a second angular vector representative of the target trajectoryaxis of the angle into two deviation angles, the length of linesrepresenting the two deviation angles are configured to be scaled toallow the user to see small deviations.
 13. The head-mounted displaysystem of claim 10, wherein the augmented reality position alignmentvisualization comprises a first color and the augmented reality angularalignment visualization comprises a different color that isdistinguishable from the first color.
 14. A method of displayingsurgical navigation information using a head-mounted display systemincluding a surgical navigation system and a surgical instrument havinga tip and at least partially defining an instrument axis in view of asurgical plan including a target trajectory axis, said methodcomprising: displaying an augmented reality position alignmentvisualization comprising two axis-aligned deviation vectors on ahead-mounted display, said two-axis aligned deviation vectors comprisinga first deviation vector and a second deviation vector wherein the firstdeviation vector and second deviation vector are representative of thedecomposition of a distance vector from a point on the target trajectoryaxis to the tip of the surgical instrument; and updating the augmentedreality position alignment visualization displayed on the head-mounteddisplay to indicate a relative location of the surgical instrument tothe target trajectory axis from the perspective of the head-mounteddisplay.
 15. The method according to claim 14, wherein the decompositionof the distance vector into two axis-aligned deviation vectors isrelative to two eigenvectors derived from: two of the three primarypatient axes derived from the orientation of the patient with thehighest angle to the target trajectory axis.
 16. The method according toclaim 14, wherein the decomposition of the distance vector into twoaxis-aligned deviation vectors is relative to two eigenvectors derivedfrom: a line of sight axis being projected onto a plane perpendicular tothe target trajectory axis and attached to the closest point on thetarget trajectory axis from the tip of the surgical instrument, and aperpendicular vector in the same plane to the projected line of sightaxis.
 17. The method according to claim 14, further comprisingdisplaying an augmented reality angular alignment visualizationcomprising a deviation angle which shows the angle between a firstangular vector representative of the axis of the surgical instrument anda second angular vector representative of the target trajectory axis.18. The method according to claim 17, further comprising updating theaugmented reality angular alignment to indicate an angle of an axis ofthe surgical instrument relative to the target trajectory axis from theperspective of the head-mounted display.
 19. The method according toclaim 17, further comprising using a first color for displaying theaugmented reality position alignment visualization or the augmentedreality angular alignment visualization and using a different color forthe other of the augmented reality position alignment visualization orthe augmented reality angular alignment visualization.
 20. The methodaccording to claim 17, further comprising highlighting the augmentedreality position alignment visualization and/or the augmented realityangular alignment visualization to the user based on the distance of thesurgical instrument to the target trajectory axis.
 21. The methodaccording to claim 14, wherein the distance between the surgicalinstrument and the target trajectory axis is computed based on thedistance of the tip of the surgical instrument to at least one basisselected from the group consisting of a segment connecting a targetobject and an entry point of the target trajectory axis, a lineconnecting the target object and the entry point of the targettrajectory axis, and the target object or the entry point of thetrajectory. 22.-45. (cancelled)